Coating for Aqueous Inkjet Transfer

ABSTRACT

An aqueous ink transfer process includes coating the surface of an image transfer member (ITM) with a coating composition to a first thickness, the coating composition including a hydrophilic composition and a surfactant, partially drying the coating composition to reduce its thickness and then applying aqueous ink onto the coating composition. The coating composition in the vicinity of the applied ink swells by absorbing water from the ink, and can further exhibit reduced adherence to the ITM. The ink is partially dried and then transferred onto a substrate.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of and claims priority to co-pendingU.S. patent application Ser. No. 14/032,996, entitled “Improved Coatingfor Aqueous Inkjet Transfer”, filed on Sep. 20, 2013, the entiredisclosure of which is incorporated herein by reference. Thisapplication cross-references co-pending U.S. patent application Ser. No.14/032,945, which is entitled “SYSTEM AND METHOD FOR IMAGE RECEIVINGSURFACE TREATMENT IN AN INDIRECT INKJET PRINTER,” and which was filed onSep. 20, 2013, the contents of which are hereby incorporated byreference in their entirety.

TECHNICAL FIELD

This disclosure relates generally to aqueous indirect inkjet printers,and, in particular, to surface preparation for aqueous ink inkjetprinting.

BACKGROUND

In general, inkjet printing machines or printers include at least oneprinthead that ejects drops or jets of liquid ink onto a recording orimage forming surface. An aqueous inkjet printer employs water-based orsolvent-based inks in which pigments or other colorants are suspended orin solution. Once the aqueous ink is ejected onto an image receivingsurface by a printhead, the water or solvent is at least partiallyevaporated to stabilize the ink image on the image receiving surface.When aqueous ink is ejected directly onto media, the aqueous ink tendsto soak into the media when it is porous, such as paper, and change thephysical properties of the media. Because the spread of the ink dropletsstriking the media is a function of the media surface properties andporosity, the print quality is inconsistent. To address this issue,indirect printers have been developed that eject ink onto a blanketmounted to a drum or endless belt. The ink is at least partially driedon the blanket and then transferred to media. Such a printer avoids thechanges in image quality, drop spread, and media properties that occurin response to media contact with the water or solvents in aqueous ink.Indirect printers also reduce the effect of variations in other mediaproperties that arise from the use of widely disparate types of paperand films used to hold the final ink images.

In aqueous ink indirect printing, an aqueous ink is jetted on to anintermediate imaging surface, typically called a blanket, and the ink ispartially dried on the blanket prior to transfixing the image to a mediasubstrate, such as a sheet of paper. To ensure excellent print qualitythe ink drops jetted onto the blanket must spread and well-coalescedprior to drying, otherwise, the ink images appear grainy and havedeletions. The lack of spreading can also cause missing or failedinkjets in the printheads to produce streaks in the ink image. Spreadingof aqueous ink is facilitated by materials having a high energy surface.In order to facilitate transfer of the ink image from the blanket to themedia substrate, however, a blanket having a surface with a relativelylow surface energy is preferred. These diametrically opposed andcompeting properties for a blanket surface make selections of materialsfor blankets difficult. Reducing ink drop surface tension helps, but thespread is still generally inadequate for appropriate image quality.

One problem confronting indirect aqueous inkjet printing processesrelates to the spread of ink drops during the printing process. Indirectimage receiving members are formed from low surface energy materialsthat promote the transfer of ink from the surface of the indirect imagereceiving member to the print medium that receives the final printedimage. Low surface energy materials, however, also tend to promote the“beading” of individual ink drops on the image receiving surface. Theresulting printed image may appear to be grainy and solid lines or solidprinted regions are reproduced as a series of dots instead of continuousfeatures in the final printed image.

An optimum blanket for an indirect image transfer process must tacklethree challenges: 1) wet image quality; 2) image transfer; and 3)print-head management. The first challenge—wet image quality—prefers ahigh surface energy density which causes the aqueous ink to spread andwet the surface, rather than beading up into discrete droplets. Thesecond challenge—image transfer—prefers that the ink, once partiallydried, has minimal attraction to the blanket surface so that 100% of theink is transferred to the media substrate. Thus, image transfer isoptimized by minimizing surface energy. The third challenge relates tohow well the print head carrying the ink jets can be kept clean of driedink. For resin-based ink, the drying of the ink on the face plate of aprint head can render it inoperable. On the other hand, too muchmoisture can condense on the face plate and cause jetting problems. Inaddition, some ink jets can be sensitive to high temperatures, typicallytemperatures above about 70° C.

Various approaches have been investigated to provide a solution thatbalances all three challenges, including blanket material selection, inkdesign and auxiliary fluid methods. With respect to material selection,materials that are known to provide optimum release properties includethe classes of silicone, fluorosilicone, TEFLON, VITON and certainhybrid materials. These compositions have low surface energy but providepoor in wetting. Alternatively, polyurethane, and polymide have beenused to improve wetting but at the cost of poor ink release properties.Tuning ink compositions to address these challenges has proven to bevery difficult since the primary performance attribute of the ink is theperformance in the print head. For instance, if the ink surface tensionis too high it will not jet properly and it if is too low it will droolout of the face plate of the print head. Compounding the problem is thefact that ink cohesion must be significantly greater than theink-to-blanket adhesion for all image contents, including the stresscases of single layer small dot and three layer process black solidprinting

Thus far, the balance between the three challenges has been elusive.Most solutions have tended to err toward optimizing image transfer fromthe blanket to the media substrate, with some sacrifice to imagequality. What is needed is a low-cost solution to this problem thatoptimizes both wet image quality and image transfer without compromisingthe ink jet print head.

SUMMARY

In one aspect, an improved coating is provided for an indirect imagereceiving member or blanket in an aqueous printing system in which thecoatings include a hydrophilic composition and a surfactant. Oneimproved coating composition includes a starch composition in a liquidcarrier as the hydrophilic composition. In certain embodiments thestarch coating composition may include a surfactant and may furtherinclude a biocide composition. The improved starch-based coatingcomposition is applied to the surface of the blanket and at leastpartially dried before the aqueous ink is applied. Ink applied in animagewise manner (i.e., according to an image transmitted to theprinting device) is at least partially dried prior to reaching thetransfer station where the ink image is transferred to a substrateconveyed between the blanket and a transfer roll. The surface of theblanket is then cleaned of any residual starch coating and ink (ifpresent) and the blanket surface continues to the next application ofthe improved starch coating composition.

In one feature of the present disclosure, the improved coatingcomposition acts as a barrier between the aqueous ink and the surface ofthe blanket to overcome high ink-blanket adhesion that otherwiseinterferes with ink transfer to the substrate. The improved coatingcompositions further ensure high image cohesion and image quality bythickening the ink-coating composite layer on the blanket surface. Theimproved coating composition is further adapted to weaken the adhesionto the blanket surface by absorption of water and/or co-solvent from theaqueous ink.

The starch composition is in a class of materials that can be dissolvedin water and that when water is subsequently removed essentially forms agel which cannot re-dissolve in water. Moreover, this class of materialsis capable of absorbing water and expanding or swelling on the surfaceof the blanket. The starch-based composition is also essentiallyimpermeable to the colorants or pigments in the aqueous ink so that thecolorants will not penetrate or absorb into the starch composition layeror skin. The starch composition thus blocks the ink colorants from theunderlying blanket, which essentially ensures complete transfer of theink color to the substrate. The swelling characteristic of thestarch-based composition causes a reduction in adherence of the layer orskin to the blanket so that a significant portion of the hydrophiliclayer/skin is transferred with the ink to the substrate.

Once the ink has been transferred the residual starch-based hydrophiliccomposition on the blanket can be easily removed by application of ashear force, such as by a wiper blade or scraper. Adding water incombination with the shearing force further facilitates removal of theresidual composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a print test comparing ink transfer onto astandard stock substrate between an untreated transfer surface and atransfer surface treated with the improved hydrophilic coatingcomposition disclosed herein, as further compared with a conventionaldirect print onto a premium photo paper.

FIG. 2 is a top view of a print test for a multilayer transfer processshowing one, two and three layer test strips printed using the improvedhydrophilic coating composition disclosed herein.

FIG. 3 is a schematic drawing of an aqueous indirect inkjet printer thatprints sheet media.

FIG. 4 is a schematic drawing of a surface maintenance unit that appliesa hydrophilic composition to a surface of an indirect image receivingmember in an inkjet printer.

FIG. 5 is a block diagram of a process for printed images in an indirectinkjet printer that uses aqueous inks.

FIG. 6A is a side view of a hydrophilic composition that is formed onthe surface of an indirect image receiving member in an inkjet printer.

FIG. 6B is a side view of dried hydrophilic composition on the surfaceof the indirect image receiving member after a dryer removes a portionof a liquid carrier in the hydrophilic composition.

FIG. 6C is a side view of a portion of an aqueous ink image that isformed on the dried hydrophilic composition on the surface of theindirect image receiving member.

FIG. 6D is a side view of a portion of the aqueous ink image that isformed on the dried hydrophilic composition after a dryer in the printerremoves a portion of the water in the aqueous ink.

FIG. 6E is a side view of a print medium that receives the aqueous inkimage and a portion of the dried layer of the hydrophilic compositionafter a transfix operation in the inkjet printer.

DETAILED DESCRIPTION

For a general understanding of the present embodiments, reference ismade to the drawings. In the drawings, like reference numerals have beenused throughout to designate like elements. As used herein, the terms“printer,” “printing device,” or “imaging device” generally refer to adevice that produces an image on print media with aqueous ink and mayencompass any such apparatus, such as a digital copier, bookmakingmachine, facsimile machine, multi-function machine, or the like, whichgenerates printed images for any purpose. Image data generally includeinformation in electronic form which are rendered and used to operatethe inkjet ejectors to form an ink image on the print media. These datacan include text, graphics, pictures, and the like. The operation ofproducing images with colorants on print media, for example, graphics,text, photographs, and the like, is generally referred to herein asprinting or marking. Aqueous inkjet printers use inks that have a highpercentage of water relative to the amount of colorant and/or solvent inthe ink.

The term “printhead” as used herein refers to a component in the printerthat is configured with inkjet ejectors to eject ink drops onto an imagereceiving surface. A typical printhead includes a plurality of inkjetejectors that eject ink drops of one or more ink colors onto the imagereceiving surface in response to firing signals that operate actuatorsin the inkjet ejectors. The inkjets are arranged in an array of one ormore rows and columns. In some embodiments, the inkjets are arranged instaggered diagonal rows across a face of the printhead. Various printerembodiments include one or more printheads that form ink images on animage receiving surface. Some printer embodiments include a plurality ofprintheads arranged in a print zone. An image receiving surface, such asan intermediate imaging surface, moves past the printheads in a processdirection through the print zone. The inkjets in the printheads ejectink drops in rows in a cross-process direction, which is perpendicularto the process direction across the image receiving surface. As used inthis document, the term “aqueous ink” includes liquid inks in whichcolorant is in a solution, suspension or dispersion with a liquidsolvent that includes water and/or one or more liquid solvents. Theterms “liquid solvent” or more simply “solvent” are used broadly toinclude compounds that may dissolve colorants into a solution, or thatmay be a liquid that holds particles of colorant in a suspension ordispersion without dissolving the colorant.

As used herein, the term “hydrophilic” refers to any composition orcompound that attracts water molecules or other solvents used in aqueousink. As used herein, a reference to a hydrophilic composition refers toa liquid carrier that carries a hydrophilic absorption agent. Examplesof liquid carriers include, but are not limited to, a liquid, such aswater or alcohol, that carries a dispersion, suspension, or solution ofan absorption agent. A dryer then removes at least a portion of theliquid carrier and the remaining solid or gelatinous phase absorptionagent has a high surface energy to absorb a portion of the water inaqueous ink drops while enabling the colorants in the aqueous ink dropsto spread over the surface of the absorption agent. As used herein, areference to a dried layer of the absorption agent refers to anarrangement of a hydrophilic compound after all or a substantial portionof the liquid carrier has been removed from the composition through adrying process. As described in more detail below, an indirect inkjetprinter forms a layer of a hydrophilic composition on a surface of animage receiving member using a liquid carrier, such as water, to apply alayer of the hydrophilic composition. The liquid carrier is used as amechanism to convey an absorption agent in the liquid carrier to animage receiving surface to form a uniform layer of the hydrophiliccomposition on the image receiving surface.

As used herein, the term “absorption agent” refers to a material that ispart of the hydrophilic composition, that has hydrophilic properties,and that is substantially insoluble to water and other solvents inaqueous ink during a printing process after the printer dries theabsorption agent into a dried layer or “skin” that covers the imagereceiving surface. The printer dries the hydrophilic composition toremove all or a portion of the liquid carrier to form a dried “skin” ofthe absorption agent on the image receiving surface. The dried layer ofthe absorption agent has a high surface energy with respect to the inkdrops that are ejected onto the image receiving surface. The highsurface energy promotes spreading of the ink on the surface of the driedlayer, and the high surface energy holds the aqueous ink in place on themoving image receiving member during the printing process.

When aqueous ink drops contact the absorption agent in the dried layer,the absorption agent absorbs a portion of the water and other solventsin the aqueous ink drop. The absorption agent in the portion of thedried layer that absorbs the water swells, but remains substantiallyintact during the printing operation and does not dissolve. Theabsorption agent in portions of the dried layer that do not contactaqueous ink has a comparatively high adhesion to the image receivingsurface and a comparatively low adhesion to a print medium, such aspaper. The portions of the dried layer that absorb water and solventsfrom the aqueous ink have a lower adhesion to the image receivingsurface, and prevent colorants and other highly adhesive components inthe ink from contacting the image receiving surface. Thus, theabsorption agent in the dried layer promotes the spread of the ink dropsto form high quality printed images, holds the aqueous ink in positionduring the printing process, promotes the transfer of the latent inkimage from the image receiving member to paper or another print medium,and promotes the separation of the print medium from the image receivingsurface after the aqueous ink image has been transferred to the printmedium.

In one aspect of the present disclosure, the layer of the hydrophiliccomposition is formed from a starch that is dissolved in a liquidcarrier such as water. The starch and liquid carrier are processed sothat the resulting composition can be applied in a thin fluid film ontothe image transfer surface or blanket and become a cross-linkedpre-gelatinized solid film when the liquid carrier is partially/mostlyremoved. When dried the composition is capable of swelling by absorbinga solvent in the ink, such as water in an aqueous ink composition, butthe composition itself does not dissolve in the solvent. The hydrophiliccomposition is applied to an image receiving surface as a liquid toenable formation of a uniform layer on the image receiving surface. Theprinter at least partially dries the hydrophilic composition to removeat least a portion of the liquid carrier from the hydrophiliccomposition to form a dried layer of solid or semi-solid absorptionagent.

Pure starch is insoluble in water but become soluble when heated. Uponheating the starch granules swell and burst, the semi-crystallinestructure of granules is lost and the starch molecules leach out of thegranules, forming a polymer solution or a gelatin structure that holdswater to thereby increase the viscosity of the composition. When wateris removed quickly, the starch does not recover its semi-crystallinestructure, and forms a cross-linked pre-gelatinized amorphous structure.When exposed to water again at relatively low temperature, thisstructure is ready to swell (absorb water) to form a gel, but will notreadily dissolve to form a solution. In a preferred embodiment, thecomposition starts as a starch solution, being dried to form across-linked pre-gelatinized amorphous structure, and subsequentlyabsorbs water/solvent from the ink to form a gel.

It is known that pure starch consists of two types of molecules: thelinear and helical amylose and the branched amylopectin. For amylose,cooling or prolonged storage of the dissolved or gelatinized starchcomposition can lead to partial recovery of the semi-crystallinestructure, causing the composition to expel carrier or water andthicken, in a process known as retrogradation and synerisis. Thisprocess can cause some quality issues for the coating and stability ofthe composition. For the branched amylopectin, retrogradation is muchless of a concern. Therefore, it is thus preferred that the compositionconsist of predominantly amylopectin.

The starch coating composition is intended to be applied to the transfersurface or blanket in a uniform film having a smoothness of opticalquality. The thickness of the film is desirably as thin as possiblewithout sacrificing the integrity of the film when exposed to ink at thejetting process. The film must also be strong enough to maintain aphysical barrier between the ink and a low surface energy transfersurface, even if weakened at the jetting process. Large starch moleculesare suitable for the strength of this film. However, some starchmolecules can swell in water with a radius of gyration greater than tensof microns, so flow coating to a few micron wet thickness isproblematic. Therefore, a control of the optimal size of starchmolecules is desired. Moreover, the gelatinized composition withsignificant amylose can create macroscopic semi-solid (gel) domains 10microns or more in size resulting in an inhomogeneous composition. Acomposition with nearly pure amylopectin starch is preferred.

In certain starch coating compositions, a surfactant can be added to thestarch and solvent (or water). The surfactant can be beneficial toimprove the wetability of the composition on a low surface energymaterial, such as silicones, TEFLON and other similar compositions. Thesurfactant can be a silicone-based polymer composition. A biocidecomposition may also be added to prevent bacterial growth, reducedegradation of the composition and improve stability and shelf life ofthe composition.

In one specific starch coating composition, about 7.3 grams of cornstarch is dispersed in about 246 grams of water and the suspension isuniformly heated at about 70° C., without boiling, to gelatinize thesuspension. In certain tests the composition gelatinized in less thanabout 2 minutes at the 70° C. temperature. In certain tests, the starchmolecules were too big and the flow property is not optimal for coating.Thus the composition is cooled to about 50° C. and then blended at highspeed for a time sufficient to reduce the gelatinized starch moleculesto a generally smaller and uniform size. In certain tests high speedmixing for about 1 minute yields generally smaller and uniformly sizedmolecules. About 0.6 g of a biocide composition, such as anantibacterial dish soap, is added, followed by about 1.2 g of asurfactant, such as Silsurf A008 surfactant. Larger quantities of thestarch coating composition may be prepared while maintaining the weightratios of the starch, water, biocide composition and surfactant. It isnoted that the biocide composition may be provided to avoid bacteriagrowth in the starch solution, thereby maintaining a good shelf life forthe composition.

It can be appreciated that in a conventional aqueous ink transfer systemthe drying step removes water from the ink image which increases imagecohesion but is often insufficient to overcome the ink-to-blanketsurface adhesion. The improved starch coating of the present systemenables 100% transfer of the ink image onto the substrate by acting as athickening agent for the ink and a release agent for the blanket orintermediate transfer surface. In particular, the starch-basedcomposition absorbs some of the water and/or co-solvent in the aqueousink, causing the starch coating layer to expand to maintain the physicalbarrier between the ink and the transfer surface. This absorptionremoves water from the ink thereby increasing the image cohesion priorto image transfer. This absorption weakens the starch coatingcomposition layer but not enough to compromise the image transferprocess. However, this weakening of the starch coating compositionsfacilitates its removal at a cleaning station by a simple wiping action,as may be accomplished by a conventional wiper blade element.

In one experiment, 1 tablespoon of corn starch was dispersed in about 1cup of water in a pan. The suspension was uniformly heated whilecontinuously stirring. The suspension began to thicken when thesuspension reached about 70° C. Stirring and heating continued for aboutanother 2 minute, without boiling. The thickened composition was cooledto about 50° C. then was blended at high speed for about 1 minute. About⅛ teaspoon of DAWN antibacterial soap concentrate was added to theblended solution, followed by about 1.2 g of Silsurf A008 surfactant(0.5%).

The starch coating composition was then applied to a flat siliconetransfer surface (RT622) using an Anilox roller and then dried to form afilm of about 0.1 micron thick. Coating, drying, ink jetting andtransfer was tested at about 21 cm/sec. The ink jetting was at 600 dpiwith a drop volume of about 5 pl. The ink is then partially dried to asemi-wet, tacky state and contact transferred to paper. As shown in FIG.1, the ink transfer on the surface treated with the improved starchcoating was significantly better than the ink transfer without thecoating. Moreover, the improved starch coating produced an ink transferthat was as good or better than a conventional ink transfer on premiumcoated photo paper. In particular, the wetting is better as evidenced bythe connected lines. In addition, although not apparent from FIG. 1, thecolor was stronger for the improved coating transfer.

Another test involved a multilayer transfer on a transfer plate (RT622)heated to about 50° C. The starch coating was first applied, followed byink transfers for magenta, yellow and cyan, after which the ink wastransferred to a conventional substrate. The results of the test shownin FIG. 2 demonstrate that the improved coating was capable of a singlelayer (magenta, yellow, cyan) transfer, a double layer transferproducing a red segment (the upper portion of the middle strip) and athree layer transfer yielding a black sample.

Several starchy materials have been tested, including corn starch,potato starch, rice starch, wheat flour, rice flour and corn flour. Allof the starches worked in the aqueous ink jet environment, although somestarches required a thicker coating while other starches required moreinvolved preparation. It was found that corn starch provided goodresults and was relatively easy to prepare. In addition, waxy starchessuch as waxy corn starch, waxy potato starch, glutinous rice starch andetc. are known to have nearly pure amylopectin. These starches producedthe best results.

It has been found that the starch coating overcomes the wet imagequality problem discussed above by providing an ink jet-required wettingsurface. In addition, the improved starch coating provides partialwater/co-solvent absorption which can be desirable for aqueous ink jetapplications. This coating improves the image cohesion significantly toenable excellent transfer of image, including hot-melt transfer at hightemperature, or sticky (semi-wet) transfer at room/warm temperatures.The starch coating reduces the total water/solvent evaporation requiredfor the process, which enables a lower (warm, 50-60C) temperature forthe blanket at the imaging point. In addition to the advantages withrespect to the three challenges discussed above, the improved coatingdisclosed herein enables simple, low-waste, low-wear and high speedcleaning/refreshing of the transfer surface, which manifests in noghosting effect and long transfer surface life.

The disclosed starch coating can further improve paper stripping. Manymaterials with good releasing properties such as silicones, graftsilicone are very tacky. Stripping is a big challenge for cut-sheetpaper handling. The starch coating stays on top of the image (on paper)and serves as an overcoat protection layer. Finally, it is believed thatthe starch coating disclosed herein is a very low-cost solution to theproblems noted above, costing as little as a few cents per Kp.

FIG. 3 illustrates a high-speed aqueous ink image producing machine orprinter 10. As illustrated, the printer 10 is an indirect printer thatforms an ink image on a surface of a blanket 21 mounted about anintermediate rotating member 12 and then transfers the ink image tomedia passing through a nip 18 formed between the blanket 21 and thetransfix roller 19. The surface 14 of the blanket 21 is referred to asthe image receiving surface of the blanket 21 and the rotating member 12since the surface 14 receives a hydrophilic composition and the aqueousink images that are transfixed to print media during a printing process.A print cycle is now described with reference to the printer 10. As usedin this document, “print cycle” refers to the operations of a printer toprepare an imaging surface for printing, ejection of the ink onto theprepared surface, treatment of the ink on the imaging surface tostabilize and prepare the image for transfer to media, and transfer ofthe image from the imaging surface to the media.

The printer 10 includes a frame 11 that supports directly or indirectlyoperating subsystems and components, which are described below. Theprinter 10 includes an indirect image receiving member, which isillustrated as rotating imaging drum 12 in FIG. 3, but can also beconfigured as a supported endless belt. The imaging drum 12 has an outerblanket 21 mounted about the circumference of the drum 12. The blanketmoves in a direction 16 as the member 12 rotates. A transfix roller 19rotatable in the direction 17 is loaded against the surface of blanket21 to form a transfix nip 18, within which ink images formed on thesurface of blanket 21 are transfixed onto a media sheet 49. In someembodiments, a heater in the drum 12 (not shown) or in another locationof the printer heats the image receiving surface 14 on the blanket 21 toa temperature in a range of approximately of 50° C. to 70° C. Theelevated temperature promotes partial drying of the liquid carrier thatis used to deposit the hydrophilic composition and of the water in theaqueous ink drops that are deposited on the image receiving surface 14.

The blanket is formed of a material having a relatively low surfaceenergy to facilitate transfer of the ink image from the surface of theblanket 21 to the media sheet 49 in the nip 18. Such materials includesilicones, fluoro-silicones, Viton, and the like. A surface maintenanceunit (SMU) 92 removes residual ink left on the surface of the blanket 21after the ink images are transferred to the media sheet 49. The lowenergy surface of the blanket does not aid in the formation of goodquality ink images because such surfaces do not spread ink drops as wellas high energy surfaces. Consequently, the SMU 92 also applies a coatingof a hydrophilic composition to the newly cleaned image receivingsurface 14 on the blanket 21. The hydrophilic composition aids inspreading aqueous ink drops on the image receiving surface and aiding inthe release of the ink image from the blanket. Examples of hydrophiliccompositions include surfactants, starches, and the like.

In one embodiment that is depicted in FIG. 4, the SMU 92 includes acoating applicator, such as a donor roller 404, which is partiallysubmerged in a reservoir 408 that holds a hydrophilic composition in aliquid carrier. The donor roller 404 rotates in response to the movementof the image receiving surface 14 in the process direction. The donorroller 404 draws the liquid hydrophilic composition from the reservoir408 and deposits a layer of the hydrophilic composition on the imagereceiving surface 14. As described below, the hydrophilic composition isdeposited as a uniform layer with a thickness of approximately 1 μm to10 μm. The SMU 92 deposits the hydrophilic composition on the imagereceiving surface 14 to form a uniform distribution of the absorptionagent in the liquid carrier of the hydrophilic composition. After adrying process, the dried layer forms a “skin” of the absorption agentthat substantially covers the image receiving surface 14 before theprinter ejects ink drops during a print process. In some illustrativeembodiments, the donor roller 404 is an anilox roller or an elastomericroller made of a material, such as rubber. The SMU 92 is operativelyconnected to a controller 80, described in more detail below, to enablethe controller to operate the donor roller, as well as a metering bladeand a cleaning blade, selectively to deposit and distribute the coatingmaterial onto the surface of the blanket and to remove un-transferredink and skin from the surface of the blanket 21.

The printer 10 includes a dryer 96 that emits heat and optionallydirects an air flow toward the hydrophilic composition that is appliedto the image receiving surface 14. The dryer 96 facilitates theevaporation of at least a portion of the liquid carrier from thehydrophilic composition to leave a dried layer of absorption agent onthe image receiving surface 14 before the image receiving member passesthe printhead modules 34A-34D to receive the aqueous printed image.

The printer 10 include an optical sensor 94A, also known as animage-on-drum (“IOD”) sensor, which is configured to detect lightreflected from the blanket surface 14 and the coating applied to theblanket surface as the member 12 rotates past the sensor. The opticalsensor 94A includes a linear array of individual optical detectors thatare arranged in the cross-process direction across the blanket 21. Theoptical sensor 94A generates digital image data corresponding to lightthat is reflected from the blanket surface 14 and the coating. Theoptical sensor 94A generates a series of rows of image data, which arereferred to as “scanlines,” as the image receiving member 12 rotates theblanket 21 in the direction 16 past the optical sensor 94A. In oneembodiment, each optical detector in the optical sensor 94A furthercomprises three sensing elements that are sensitive to wavelengths oflight corresponding to red, green, and blue (RGB) reflected lightcolors. Alternatively, the optical sensor 94A includes illuminationsources that shine red, green, and blue light or, in another embodiment,the sensor 94A has an illumination source that shines white light ontothe surface of blanket 21 and white light detectors are used. Theoptical sensor 94A shines complementary colors of light onto the imagereceiving surface to enable detection of different ink colors using thephotodetectors. The image data generated by the optical sensor 94A isanalyzed by the controller 80 or other processor in the printer 10 toidentify the thickness of the coating on the blanket and the areacoverage. The thickness and coverage can be identified from eitherspecular or diffuse light reflection from the blanket surface and/orcoating. Other optical sensors, such as 94B, 94C, and 94D, are similarlyconfigured and can be located in different locations around the blanket21 to identify and evaluate other parameters in the printing process,such as missing or inoperative inkjets and ink image formation prior toimage drying (94B), ink image treatment for image transfer (94C), andthe efficiency of the ink image transfer (94D). Alternatively, someembodiments can include an optical sensor to generate additional datathat can be used for evaluation of the image quality on the media (94E).

The printer 10 includes an airflow management system 100, whichgenerates and controls a flow of air through the print zone. The airflowmanagement system 100 includes a printhead air supply 104 and aprinthead air return 108. The printhead air supply 104 and return 108are operatively connected to the controller 80 or some other processorin the printer 10 to enable the controller to manage the air flowingthrough the print zone. This regulation of the air flow can be throughthe print zone as a whole or about one or more printhead arrays. Theregulation of the air flow helps prevent evaporated solvents and waterin the ink from condensing on the printhead and helps attenuate heat inthe print zone to reduce the likelihood that ink dries in the inkjets,which can clog the inkjets. The airflow management system 100 can alsoinclude sensors to detect humidity and temperature in the print zone toenable more precise control of the temperature, flow, and humidity ofthe air supply 104 and return 108 to ensure optimum conditions withinthe print zone. Controller 80 or some other processor in the printer 10can also enable control of the system 100 with reference to ink coveragein an image area or even to time the operation of the system 100 so aironly flows through the print zone when an image is not being printed.

The high-speed aqueous ink printer 10 also includes an aqueous inksupply and delivery subsystem 20 that has at least one source 22 of onecolor of aqueous ink. Since the illustrated printer 10 is a multicolorimage producing machine, the ink delivery system 20 includes four (4)sources 22, 24, 26, 28, representing four (4) different colors CYMK(cyan, yellow, magenta, black) of aqueous inks. In the embodiment ofFIG. 3, the printhead system 30 includes a printhead support 32, whichprovides support for a plurality of printhead modules, also known asprint box units, 34A through 34D. Each printhead module 34A-34Deffectively extends across the width of the blanket and ejects ink dropsonto the surface 14 of the blanket 21. A printhead module can include asingle printhead or a plurality of printheads configured in a staggeredarrangement. Each printhead module is operatively connected to a frame(not shown) and aligned to eject the ink drops to form an ink image onthe coating on the blanket surface 14. The printhead modules 34A-34D caninclude associated electronics, ink reservoirs, and ink conduits tosupply ink to the one or more printheads. In the illustrated embodiment,conduits (not shown) operatively connect the sources 22, 24, 26, and 28to the printhead modules 34A-34D to provide a supply of ink to the oneor more printheads in the modules. As is generally familiar, each of theone or more printheads in a printhead module can eject a single color ofink. In other embodiments, the printheads can be configured to eject twoor more colors of ink. For example, printheads in modules 34A and 34Bcan eject cyan and magenta ink, while printheads in modules 34C and 34Dcan eject yellow and black ink. The printheads in the illustratedmodules are arranged in two arrays that are offset, or staggered, withrespect to one another to increase the resolution of each colorseparation printed by a module. Such an arrangement enables printing attwice the resolution of a printing system only having a single array ofprintheads that eject only one color of ink. Although the printer 10includes four printhead modules 34A-34D, each of which has two arrays ofprintheads, alternative configurations include a different number ofprinthead modules or arrays within a module.

After the printed image on the blanket surface 14 exits the print zone,the image passes under an image dryer 130. The image dryer 130 includesa heater, such as a radiant infrared, radiant near infrared and/or aforced hot air convection heater 134, a dryer 136, which is illustratedas a heated air source 136, and air returns 138A and 138B. The infraredheater 134 applies infrared heat to the printed image on the surface 14of the blanket 21 to evaporate water or solvent in the ink. The heatedair source 136 directs heated air over the ink to supplement theevaporation of the water or solvent from the ink. In one embodiment, thedryer 136 is a heated air source with the same design as the dryer 96.While the dryer 96 is positioned along the process direction to dry thehydrophilic composition, the dryer 136 is positioned along the processdirection after the printhead modules 34A-34D to at least partially drythe aqueous ink on the image receiving surface 14. The air is thencollected and evacuated by air returns 138A and 138B to reduce theinterference of the air flow with other components in the printing area.

As further shown, the printer 10 includes a recording media supply andhandling system 40 that stores, for example, one or more stacks of papermedia sheets of various sizes. The recording media supply and handlingsystem 40, for example, includes sheet or substrate supply sources 42,44, 46, and 48. In the embodiment of printer 10, the supply source 48 isa high capacity paper supply or feeder for storing and supplying imagereceiving substrates in the form of cut media sheets 49, for example.The recording media supply and handling system 40 also includes asubstrate handling and transport system 50 that has a mediapre-conditioner assembly 52 and a media post-conditioner assembly 54.The printer 10 includes an optional fusing device 60 to apply additionalheat and pressure to the print medium after the print medium passesthrough the transfix nip 18. In the embodiment of FIG. 3, the printer 10includes an original document feeder 70 that has a document holding tray72, document sheet feeding and retrieval devices 74, and a documentexposure and scanning system 76.

Operation and control of the various subsystems, components andfunctions of the machine or printer 10 are performed with the aid of acontroller or electronic subsystem (ESS) 80. The ESS or controller 80 isoperably connected to the image receiving member 12, the printheadmodules 34A-34D (and thus the printheads), the substrate supply andhandling system 40, the substrate handling and transport system 50, and,in some embodiments, the one or more optical sensors 94A-94E. The ESS orcontroller 80, for example, is a self-contained, dedicated mini-computerhaving a central processor unit (CPU) 82 with electronic storage 84, anda display or user interface (UI) 86. The ESS or controller 80, forexample, includes a sensor input and control circuit 88 as well as apixel placement and control circuit 89. In addition, the CPU 82 reads,captures, prepares and manages the image data flow between image inputsources, such as the scanning system 76, or an online or a work stationconnection 90, and the printhead modules 34A-34D. As such, the ESS orcontroller 80 is the main multi-tasking processor for operating andcontrolling all of the other machine subsystems and functions, includingthe printing process discussed below.

The controller 80 can be implemented with general or specializedprogrammable processors that execute programmed instructions. Theinstructions and data required to perform the programmed functions canbe stored in memory associated with the processors or controllers. Theprocessors, their memories, and interface circuitry configure thecontrollers to perform the operations described below. These componentscan be provided on a printed circuit card or provided as a circuit in anapplication specific integrated circuit (ASIC). Each of the circuits canbe implemented with a separate processor or multiple circuits can beimplemented on the same processor. Alternatively, the circuits can beimplemented with discrete components or circuits provided in very largescale integrated (VLSI) circuits. Also, the circuits described hereincan be implemented with a combination of processors, ASICs, discretecomponents, or VLSI circuits.

Although the printer 10 in FIG. 3 is described as having a blanket 21mounted about an intermediate rotating member 12, other configurationsof an image receiving surface can be used. For example, the intermediaterotating member can have a surface integrated into its circumferencethat enables an aqueous ink image to be formed on the surface.Alternatively, a blanket is configured as an endless rotating belt forformation of an aqueous image. Other variations of these structures canbe configured for this purpose. As used in this document, the term“intermediate imaging surface” includes these various configurations.

Once an image or images have been formed on the blanket and coatingunder control of the controller 80, the illustrated inkjet printer 10operates components within the printer to perform a process fortransferring and fixing the image or images from the blanket surface 14to media. In the printer 10, the controller 80 operates actuators todrive one or more of the rollers 64 in the media transport system 50 tomove the media sheet 49 in the process direction P to a positionadjacent the transfix roller 19 and then through the transfix nip 18between the transfix roller 19 and the blanket 21. The transfix roller19 applies pressure against the back side of the recording media 49 inorder to press the front side of the recording media 49 against theblanket 21 and the image receiving member 12. Although the transfixroller 19 can also be heated, in the exemplary embodiment of FIG. 3, thetransfix roller 19 is unheated. Instead, the pre-heater assembly 52 forthe media sheet 49 is provided in the media path leading to the nip. Thepre-conditioner assembly 52 conditions the media sheet 49 to apredetermined temperature that aids in the transferring of the image tothe media, thus simplifying the design of the transfix roller. Thepressure produced by the transfix roller 19 on the back side of theheated media sheet 49 facilitates the transfixing (transfer and fusing)of the image from the image receiving member 12 onto the media sheet 49.The rotation or rolling of both the image receiving member 12 andtransfix roller 19 not only transfixes the images onto the media sheet49, but also assists in transporting the media sheet 49 through the nip.The image receiving member 12 continues to rotate to enable the printingprocess to be repeated.

After the image receiving member moves through the transfix nip 18, theimage receiving surface passes a cleaning unit that removes residualportions of the absorption agent and small amounts of residual ink fromthe image receiving surface 14. In the printer 10, the cleaning unit isembodied as a cleaning blade 95 that engages the image receiving surface14. The blade 95 is formed from a material that wipes the imagereceiving surface 14 without causing damage to the blanket 21. Forexample, the cleaning blade 95 is formed from a flexible polymermaterial in the printer 10. As depicted below in FIG. 3, anotherembodiment has a cleaning unit that includes a roller or other memberthat applies a mixture of water and detergent to remove residualmaterials from the image receiving surface 14 after the image receivingmember moves through the transfix nip 18. As used herein, the term“detergent” or cleaning agent refers to any surfactant, solvent, orother chemical compound that is suitable for removing the dried portionof the absorption agent and any residual ink that may remain on theimage receiving surface from the image receiving surface. One example ofa suitable detergent is sodium stearate, which is a compound commonlyused in soap. Another example is IPA, which is common solvent that isvery effective to remove ink residues from the image receiving surface.

FIG. 5 depicts a process 700 for operating an aqueous indirect inkjetprinter using a hydrophilic composition to form a dried coating or“skin” layer of a dried absorption agent in the hydrophilic compositionon an image receiving surface of an indirect image receiving memberprior to ejecting liquid ink drops onto the dried layer. In thediscussion below, a reference to the process 700 performing an action orfunction refers to a controller, such as the controller 80 in theprinter 10, executing stored programmed instructions to perform theaction or function in conjunction with other components of the printer.The process 700 is described in conjunction with FIG. 1 showing theprinter 10, and FIG. 6A-FIG. 6E showing the blanket and coatings, forillustrative purposes.

Process 700 begins as the printer applies a layer of a hydrophiliccomposition with a liquid carrier to the image receiving surface of theimage receiving member (block 704). In the printer 10, the drum 12 andblanket 21 move in the process direction along the indicated circulardirection 16 during the process 700 to receive the hydrophiliccomposition. In the printer 10, the SMU 92 applies a hydrophiliccomposition with a liquid carrier to the surface 14 of the imaging drum12.

In one embodiment, the liquid carrier is water or another liquid, suchas alcohol, which partially evaporates from the image receiving surfaceand leaves a dried layer of absorption agent on the image receivingsurface. In FIG. 6A, the surface of the indirect image receiving member504 is covered with the hydrophilic composition 508. The SMU 92 depositsthe hydrophilic composition on the image receiving surface 14 of theblanket 21 to form a uniform coating of the hydrophilic composition. Agreater coating thickness of the hydrophilic composition enablesformation of a uniform layer that completely covers the image receivingsurface, but the increased volume of liquid carrier in the thickercoating requires additional drying time or larger dryers to remove theliquid carrier to form a dried layer of the absorption agent. Thinnercoatings of the hydrophilic composition require the removal of a smallervolume of the liquid carrier to form the dried layer, but if the coatingof hydrophilic composition is too thin, then the coating may not fullycover the image receiving surface. In certain embodiments thehydrophilic composition with the liquid carrier is applied at athickness of between approximately 1 μm and 10 μm.

Process 700 continues as a dryer in the printer dries the hydrophiliccomposition to remove at least a portion of the liquid carrier and toform a dried layer of the absorption agent on the image receivingsurface (block 708). In the printer 10 the dryer 96 applies radiant heatand optionally includes a fan to circulate air onto the image receivingsurface of the drum 12 or belt 13. FIG. 6B depicts the dried layer ofthe absorption agent 512. The dryer 96 removes a portion of the liquidcarrier, which decreases the thickness of the layer of dried layer thatis formed on the image receiving surface. In the printer 10 thethickness of the dried layer 512 is on the range of 0.1 μm to 3 μm indifferent embodiments, and in certain specific embodiments between 0.1to 0.5 μm.

The dried layer of the absorption agent 512 is also referred to as a“skin” layer. The dried layer 512 has a uniform thickness that coverssubstantially all of the portion of the image receiving surface thatreceives aqueous ink during a printing process. As described above,while the hydrophilic composition with the liquid carrier includessolutions, suspension, or dispersion of the hydrophilic material in aliquid carrier, the dried layer of the absorption agent 512 forms acontinuous matrix that covers the image receiving surface 504. The driedlayer 512 has a comparatively high level of adhesion to the imagereceiving surface 504, and a comparatively low level of adhesion to aprint medium that contacts the dried layer 512. As described in moredetail below, when aqueous ink drops are ejected onto portions of thedried layer 512, a portion of the water and other solvents in theaqueous ink permeates the dried layer 512. The portion of the driedlayer 512 that absorbs the liquid swells, but remains substantiallyintact on the image receiving surface 504.

Process 700 continues as the image receiving surface with thehydrophilic skin layer moves past one or more printheads that ejectaqueous ink drops onto the dried layer and the image receiving surfaceto form a latent aqueous printed image (block 712). The printheadmodules 34A-34D in the printer 10 eject ink drops in the CMYK colors toform the printed image. When the water in the aqueous ink contacts thedried layer of the absorption agent that is formed on the imagereceiving surface, the dried layer rapidly absorbs the liquid water.Thus, each ink drop of the aqueous ink that is ejected into the imagereceiving surface expands as the absorption agent in the dried layerabsorbs a portion of the water in the liquid ink drop. The absorption ofwater into the dried layer 512 also promotes binding between the aqueousink and the absorption agent in the dried layer to “pin” or hold theliquid ink in a single location on the image receiving surface 504.

As depicted in FIG. 6C, the portion of the dried layer 512 that receivesaqueous ink 524 absorbs water from the aqueous ink and swells, as isdepicted by the region 520. The absorption agent in the region 520absorbs water and other solvents in the ink and the absorption agentswells in response to absorption of the water and solvent. The aqueousink 524 includes colorants such as pigments, resins, polymers, and thelike. The absorption agent 512 is substantially impermeable to thecolorants in the ink 524, and the colorants remain on the surface of thedried layer 512 where the aqueous ink spreads. Since the dried layer 512is typically less than 1 μm in thickness, the absorption agent in thedried layer 520 absorbs only a portion of the water from the aqueous ink524, while the ink 524 retains a majority of the water.

The spread of the liquid ink enables neighboring aqueous ink drops tomerge together on the image receiving surface instead of beading intoindividual droplets as occurs in traditional low-surface energy imagereceiving surfaces. In the example shown in FIG. 1 the ink drops thatare formed on a bare image receiving surface with low-surface energy andno coating, and then are transferred to ordinary paper exhibit beadingof the ink drops in which the drops remain in the form of individualdroplets instead of merging together. When the printed ink drops thatare jetted directly to a high-quality paper that is specifically coatedfor inkjet printing the ink drops spread to a greater degree, but thepaper absorbs a large proportion of the colorant in the ink quickly,which reduces the perceptible density of the ink. The quick and completeabsorption of the ink drops into the premium paper limits the amount ofspreading of the ink drops, resulting in a printed pattern that stillincludes non-continuous lines. However, the middle printed pattern isformed using the hydrophilic composition described above. As depicted inFIG. 1, the ink drops spread because the absorption agent has a highsurface energy that promotes spreading of the ink drops on the imagereceiving member. Furthermore, slow absorption of the water/solvent bythe skin and the limited water absorption capacity of the skin give theink more time to spread. Thus, the dried layer enables printing of solidlines and patterns as depicted in FIG. 1 using less ink than is requiredwith prior art printers.

Referring again to FIG. 5, the process 700 continues with a partialdrying process of the aqueous ink on the image receiving member (block716). The drying process removes a portion of the water from the aqueousink and the hydrophilic skin layer on the image receiving surface sothat the amount of water that is transferred to a print medium in theprinter does not produce cockling or other deformations of the printmedium. In the printer 10, the heated air source 136 directs heated airtoward the image receiving surface 14 to dry the printed aqueous inkimage. In some embodiments, the image receiving member and blanket areheated to an elevated temperature to promote evaporation of liquid fromthe ink and the dried layer of the absorption agent. For example, in theprinter 10, the imaging drum 12 and blanket 21 are heated to atemperature of 50° C. to 70° C. to enable partial drying of the ink andabsorption agent in the dried layer during the printing process. Asdepicted in FIG. 6D, the drying process forms a partially dried layer528 and aqueous ink 532 that both retain a reduced amount of watercompared to the freshly printed aqueous ink image of FIG. 6C.

The drying process increases the viscosity of the aqueous ink, whichchanges the consistency of the aqueous ink from a low-viscosity liquidto a higher viscosity tacky material. In some embodiments, theabsorption agent that absorbs a portion of the water in the aqueous inkalso acts as a thickening agent that increases the viscosity of theaqueous ink. The drying process also reduces the thickness of the ink532 and the portion of the absorption agent 528 that absorbed water fromthe ink 532. One common failure mode for transfer of aqueous ink imagesto print media occurs when the aqueous ink image splits. That is to say,only about half of the ink transfers to the print medium from theindirect image receiving surface, while the remaining portion of the inkimage remains on the indirect image receiving member. The failure of inktransfer is typically caused by the low cohesion of ink image layer,because the ink layer has the weakest separation force at the exit ofthe transfer nip when two image receiving surface and the substratesurface are separating. To increase the efficiency of ink transfer, thecohesion of the ink layer or ink/skin composite layer should besignificantly greater than the adhesion between the skin and the blanketsurface. As is known in the art, the cohesion of the ink is proportionalto the viscosity of the ink and inversely proportional to the thicknessof the ink. Thus, the drying process greatly increases the cohesivenessof the aqueous ink. The materials in the ink 532 with the highest degreeof cohesiveness include resins or polymers that do not permeate into theunderlying absorption agent 528. The underlying layer of the absorptionagent 528 separates the partially dried ink 532 from the image receivingsurface 504, and the water content in the absorption agent 528 reducesthe adhesion between the absorption agent 528 and the image receivingsurface 504. Thus, the partially dried ink 532 and absorption agent 528enable efficient transfer of the printed ink from the image receivingsurface 504 to a print medium.

Process 700 continues as the printer transfixes the latent aqueous inkimage from the image receiving surface to a print medium, such as asheet of paper (block 720). In the printer 10, the image receivingsurface 14 of the drum 12 engages the transfix roller 19 to form a nip18. A print medium, such as a sheet of paper, moves through the nipbetween the drum 12 and the transfix roller 19. The pressure in the niptransfers the latent aqueous ink image and a portion of the dried layerto the print medium. After passing through the transfix nip 18, theprint medium carries the printed aqueous ink image. As depicted in FIG.6E, a print medium 536 carries a printed aqueous ink image 532 with theabsorption agent 528 covering the ink image 532 on the surface of theprint medium 536. The absorption agent 528 provides protection to theaqueous ink image from scratches or other physical damage while theaqueous ink image 532 dries on the print medium 536.

As depicted in FIG. 6E, the aqueous ink and portions of the dried layerthat absorb ink separate from the image receiving surface 504 in thetransfix nip since the image receiving surface 504 has a low level ofadhesion to the absorption agent 528 that is formed under the printedink image 532. The dry portions of the absorption agent in the driedlayer 512 have minimal adhesion to the print medium 536, which promotesthe separation of the print medium 536 from the image receiving surface504 after completion of the transfix process. By contrast, prior artrelease agents, such as silicone oil, promote the release of ink from animage receiving surface, but also form an adhesive layer between theimage receiving member and the print medium, which presents difficultyin separating the print medium from the image receiving member after thetransfix operation. As depicted in FIG. 6E, the dry portions of theabsorption agent in the dried layer 512 typically remains on the imagereceiving surface 504 after completion of the transfix operation becausethe absorption agent has a low level of adhesion to the print medium.

During process 700, the printer cleans residual portions of theabsorption agent in the dried layer from the image receiving surfaceafter the transfixing operation (block 724). In one embodiment, a fluidcleaning system 395 uses, for example, a combination of water and adetergent with mechanical agitation on the image receiving surface toremove the residual portions of the absorption agent from the surface ofthe belt 13. The fluid cleaning system 395 uses, for example, acombination of water and a detergent to remove the residual portions ofthe absorption agent from the surface of the belt 13. In the printer 10,a cleaning blade 95, which can be used in conjunction with water,engages the blanket 21 to remove the residual absorption agent from theimage receiving surface 14. The cleaning blade 95 is, for example, apolymer blade that wipes residual portions of the absorption agent fromthe blanket 21.

During a printing operation, process 700 returns to the processingdescribed above with reference to block 704 to apply the hydrophiliccomposition to the image receiving surface, print additional aqueous inkimages, and transfix the aqueous ink images to print media foradditional printed pages in the print process. The illustrativeembodiment of the printer 10 operates in a “single pass” mode that formsthe dried layer, prints the aqueous ink image and transfixes the aqueousink image to a print medium in a single rotation or circuit of theindirect image receiving member. In alternative embodiments, an inkjetemploys a multi-pass configuration where the image receiving surfacecompletes two or more rotations or circuits to form the dried layer andreceive the aqueous ink image prior to transfixing the printed image tothe print medium.

In some embodiments of the process 700, the printer forms printed imagesusing a single layer of ink such as the ink that is depicted in FIG. 6C.In the printer 10, however, the multiple printhead modules enable theprinter to form printed images with multiple colors of ink. In otherembodiments of the process 700, the printer forms images using multipleink colors. In some regions of the printed image, multiple colors of inkmay overlap in the same area on the image receiving surface, formingmultiple ink layers on the hydrophilic composition layer. The methodsteps in FIG. 5 can be applied to the multiple ink layer circumstancewith the same results, as demonstrated by the multiple layer test stripsshown in FIG. 2.

It will be appreciated that variations of the above-disclosed apparatusand other features, and functions, or alternatives thereof, may bedesirably combined into many other different systems or applications.Various presently unforeseen or unanticipated alternatives,modifications, variations, or improvements therein may be subsequentlymade by those skilled in the art, which are also intended to beencompassed by the following claims.

What is claimed is:
 1. An aqueous ink transfer process comprising:coating the surface of an image transfer member (ITM) with a coatingcomposition to a first thickness, the coating composition including ahydrophilic composition and a surfactant; partially drying the coatingcomposition to a reduced second thickness; applying aqueous ink onto thecoating composition; swelling the coating composition by absorbing waterfrom the ink; partially drying the ink; and transferring the ink onto asubstrate.
 2. The aqueous ink transfer process of claim 1, wherein thefirst thickness is between 1 μm and 10 μm.
 3. The aqueous ink transferprocess of claim 2 wherein the second thickness of between 0.1 μm and 1μm.
 4. The aqueous ink transfer process of claim 1, wherein the step oftransferring the ink onto a substrate includes transferring part of thecoating composition swollen by absorbing water from the ink with theink.
 5. The aqueous ink transfer process of claim 1, wherein the surfaceof the ITM has a low surface energy.
 6. The aqueous ink transfer processof claim 1, wherein the step of applying aqueous ink includes applyingthe ink in an imagewise manner.
 7. The aqueous ink transfer process ofclaim 1, in which the aqueous ink includes a colorant in a liquidsolvent, wherein the hydrophilic composition includes an absorptionagent in a liquid carrier, the absorption agent adapted to absorb thesolvent in the aqueous ink.
 8. The aqueous ink transfer process of claim7, wherein the absorption agent includes a starch.
 9. The aqueous inktransfer process of claim 8, wherein the starch is a starch consistingof predominantly amylopectin.
 10. The aqueous ink transfer process ofclaim 8, wherein the starch includes a starch selected from the groupincluding corn starch, potato starch, rice starch, wheat flour, riceflour and corn flour.
 11. An aqueous ink transfer process comprising:coating the surface of an image transfer member (ITM) with a coatingcomposition, the coating composition including a hydrophilic compositionand a surfactant; applying aqueous ink onto the coating composition;after applying the ink, reducing the adherence of the coatingcomposition to the surface of the ITM at the location of the appliedink; partially drying the ink; and transferring the ink onto asubstrate.
 12. The aqueous ink transfer process of claim 11, wherein thesurface of the ITM has a low surface energy.
 13. The aqueous inktransfer process of claim 11, wherein the step of transferring the inkonto a substrate includes transferring part of the coating compositionhaving reduced adherence to the surface of the ITM.
 14. An aqueous inktransfer process comprising: coating the surface of an image transfermember (ITM) with a coating composition including a hydrophiliccomposition and a surfactant; applying aqueous ink onto the coatingcomposition; absorbing water from the ink into the coating contacted bythe ink; partially drying the ink to remove additional water from theink; and transferring the ink onto a substrate.
 15. The aqueous inktransfer process of claim 14, wherein the step of transferring the inkonto a substrate includes transferring part of the coating compositioncontacted by the ink with the ink.
 16. The aqueous ink transfer processof claim 14, wherein the surface of the ITM has a low surface energy.17. The aqueous ink transfer process of claim 14, in which the aqueousink includes a colorant in a liquid solvent, wherein the hydrophiliccomposition includes an absorption agent in a liquid carrier, theabsorption agent adapted to absorb the solvent in the aqueous ink. 18.The aqueous ink transfer process of claim 17, wherein the absorptionagent includes a starch.